rust-galmon-web/src/ui/main/world_geo/clip_antimeridian.rs

use super::{
	Cartesian,
	Clip,
	ClipControl,
	Clipper,
	PathClipper,
	RadianPoint,
	DrawPath,
	F32_PRECISION,
};

fn _clip_longitude_degeneracies(p: RadianPoint) -> RadianPoint {
	use std::f32::consts::PI;

	let border = PI.copysign(p.lambda);
	if (p.lambda - border).abs() < F32_PRECISION {
		RadianPoint {
			lambda: p.lambda - (border * F32_PRECISION),
			phi: p.phi,
		}
	} else {
		p
	}
}

// line from a to b crosses antimeridian: calculate at which latitude ("phi") it intersects.
fn _clip_antimeridian_intersect(a: RadianPoint, b: RadianPoint) -> f32 {
	let a = _clip_longitude_degeneracies(a);
	let b = _clip_longitude_degeneracies(b);

	let x = Cartesian::from(a);
	let y = Cartesian::from(b);

	let result_adjacent = x.b * y.a - y.b * x.a;

	if result_adjacent.abs() > F32_PRECISION {
		let result_opposite = x.c * y.b - y.c * x.b;
		(result_opposite / result_adjacent).atan()
	} else {
		(a.phi + b.phi) * 0.5
	}
}

pub struct ClipAntimeridian;

impl ClipAntimeridian {
	#[allow(unused)]
	pub fn new<S>(sink: S) -> Clip<S, ClipAntimeridian>
	where
		S: DrawPath<Point = RadianPoint>,
	{
		Clip::new(sink, ClipAntimeridian)
	}
}

impl Clipper for ClipAntimeridian {
	type PathClipper = ClipAntimeridianPathClipper;

	fn create_clipper(&self) -> Self::PathClipper {
		ClipAntimeridianPathClipper {
			first_prev: None
		}
	}

	fn interpolate<S>(&self, control: &mut ClipControl<S>, from_to: Option<(RadianPoint, RadianPoint)>, forward: bool)
	where
		S: DrawPath<Point = RadianPoint>,
	{
		use std::f32::consts::{PI, FRAC_PI_2};
		let forward_sign = if forward { 1.0 } else { -1.0 };

		if let Some((from, to)) = from_to {
			if (to.lambda - from.lambda).abs() > PI {
				// crossing antimeridian
				let lambda = PI.copysign(to.lambda - from.lambda);
				let phi = forward_sign * lambda / 2.0;
				control.line(RadianPoint { lambda: -lambda, phi }, false);
				control.line(RadianPoint { lambda: 0.0, phi }, false);
				control.line(RadianPoint { lambda: lambda, phi }, false);
			} else {
				control.line(to, false);
			}
		} else {
			let phi = forward_sign * FRAC_PI_2;
			control.line(RadianPoint { lambda: -PI, phi:  phi }, false);
			control.line(RadianPoint { lambda: 0.0, phi:  phi }, false);
			control.line(RadianPoint { lambda:  PI, phi:  phi }, false);
			control.line(RadianPoint { lambda:  PI, phi:  0.0 }, false);
			control.line(RadianPoint { lambda:  PI, phi: -phi }, false);
			control.line(RadianPoint { lambda: 0.0, phi: -phi }, false);
			control.line(RadianPoint { lambda: -PI, phi: -phi }, false);
			control.line(RadianPoint { lambda: -PI, phi:  0.0 }, false);
			control.line(RadianPoint { lambda: -PI, phi:  phi }, false);
		}
	}
}

pub struct ClipAntimeridianPathClipper {
	first_prev: Option<((RadianPoint, bool), bool, RadianPoint)>,
}

impl PathClipper for ClipAntimeridianPathClipper {
	fn line<S>(&mut self, control: &mut ClipControl<S>, next: RadianPoint, stroke: bool)
	where
		S: DrawPath<Point = RadianPoint>,
	{
		use std::f32::consts::{PI, FRAC_PI_2};

		let next_positive = next.lambda > 0.0;

		if let Some(((first, first_stroke), prev_positive, prev)) = &mut self.first_prev {
			let delta = (next.lambda - prev.lambda).abs();
			if (delta - PI).abs() < F32_PRECISION { // line crosses a pole
				// north or south?
				let phi_side = if (prev.phi + next.phi) > 0.0 { FRAC_PI_2 } else { -FRAC_PI_2 };
				// go to pole on same latitude as prev point
				control.line(RadianPoint { lambda: prev.lambda, phi: phi_side }, stroke);
				// then to the "nearer" side (east/west), still at the pole ("same point", but projection might differ)
				control.line(RadianPoint { lambda: PI.copysign(prev.lambda), phi: phi_side }, false);
				control.split_path();
				// start at side (east/west), but at pole
				*first = RadianPoint { lambda: PI.copysign(next.lambda), phi: phi_side };
				*first_stroke = stroke;
				control.line(*first, false);
				// move to pole on same latitude as next point
				control.line(RadianPoint { lambda: next.lambda, phi: phi_side }, false);
			} else if *prev_positive != next_positive && delta >= PI { // line crosses antimeridian
				// get latitude for the intersection
				let phi_side = _clip_antimeridian_intersect(*prev, next);
				// move to intersection on prev side
				control.line(RadianPoint { lambda: PI.copysign(prev.lambda), phi: phi_side }, stroke);
				control.split_path();
				// start at intersection on next side
				*first = RadianPoint { lambda: PI.copysign(next.lambda), phi: phi_side };
				*first_stroke = stroke;
				control.line(*first, false);
			}

			*prev_positive = next_positive;
			*prev = next;
		} else {
			self.first_prev = Some(((next, stroke), next_positive, next));
		}
		control.line(next, stroke);
	}
}